|Year|Title|System|Developer|Publisher|
|---|---|---|---|---|
|1984|Ghostbusters|Atari 800, Commodore 64, MSX, ZX Spectrum, Amstrad CPC|Activision|Activision|
|1985|Ghostbusters|Atari 2600, Apple II|Activision|Activision|
|1987|The Real Ghostbusters|Arcade|Data East|Data East|
|1987|Ghostbusters|Sega Master System|Activision|Sega|
|1988|Ghostbusters|NES|Bits Laboratory|Activision/Tokuma Shoten|
|1989|The Real Ghostbusters|Commodore 64, Amiga, ZX Spectrum, Amstrad CPC, Atari ST|Data East|Activision|
|1989|Ghostbusters II|Atari 2600, Amiga, Commodore 64, MSX, PC, ZX Spectrum, Amstrad CPC|Activision|Activision|
|1990|Ghostbusters II|NES|Kemco|Activision|
|1990|Ghostbusters|Sega Mega Drive/Genesis|Sega|Sega|
|1990|New Ghostbusters 2|Game Boy, NES|Hal Laboratory|Activision|
|1993|The Real Ghostbusters|Game Boy|Kemco|Activision|
|2009|Ghostbusters: The Video Game|PlayStation 3, PlayStation 2, PlayStation Portable, Xbox 360, Nintendo DS, Wii, PC|Terminal Reality, Red Fly Studios, Zen Studios|Atari, Sony Computer Entertainment (Europe only, PS2 and PS3 versions)|
|2011|Ghostbusters: Sanctum of Slime|PlayStation Network, Xbox Live, PC|Behaviour Interactive|Atari|
|2012|Ghostbusters: Paranormal Blast|Android, iOS|XMG Studio||
|2013|Ghostbusters|iOS|Beeline Interactive|Capcom|

Question: what is the total amount of games activision developed?
Answer: 4